Groundwater sampling in Feb. 2013, confirmed tetrachloroethene (PCE), Trichloroethene (TCE), Vinyl chloride (VC) and Cis-1,2-dicholoroethene (c-1,2-DCE) are not detected above the laboratory reporting limit of 0.5 micrograms per liter (µg/l) in any of the five wells sampled at the site.

Detected concentrations of PCE, TCE, VC and c-1,2-DCE have been below their respective Aquifer Water Quality Standard (AWQSs) since the June 2006 groundwater sampling event. Historical groundwater monitoring data suggests that monitored natural attenuation (MNA) achieved cleanup of the site to concentrations below AWQSs.

ADEQ has reviewed the remedy and determined that site completion criteria has been met and that cleanup levels have been achieved. On December 27, 2013, ADEQ issued a closeout Record of Decision (ROD) demonstrating that the site completion criteria used to evaluate the selected remedial action for volatile organic compound (VOC) contaminated groundwater at the site has been achieved. The decision in the closeout ROD is based upon previous activities and investigations conducted and performed for this site.

Community Involvement Activities:

A CAB was formed for the site in conjunction with the Payson PCE site and met on a regular basis throughout the remedial investigation (RI) process. Their final meeting was held in November 2008 where ADEQ presented the final ROD for the site.

Site History:

1984: Grand Way Cleaners (GWC) began operations at the Bonanza Square location.

1995-1998: In July and November 1998, ADEQ conducted a video inspection of the sewer line and collected soil and soil vapor samples where the video indicated breaks in the line. In 1997, PCE was detected in three domestic wells near GWC. In March 1995, ADEQ conducted soil and soil vapor sampling of the area around GWC.

2000: In September, passive soil gas samples were collected throughout the Bonanza Square property to identify the source area(s). Two potential source areas were identified: 1) beneath GWC, and 2) near the location of an abandoned septic system.

2001: In February, three groundwater monitor wells were drilled and installed. In November, three nested vapor wells and an angled groundwater monitor well were installed at the Bonanza Square property. Vapor samples collected indicated high concentrations of PCE beneath the GWC location.

2002: In September, the draft RI report was released for public comment.

2003: Concentrations of PCE have decreased since 1997. However, in March, concentrations of TCE, cis-1,2-DCE, and VC increased in the groundwater monitor well beneath GWC due to the breakdown of PCE.

2006: Concentrations of PCE in monitor wells at the site have generally decreased from 24 µg/l in March 2001 to less than 5.0 µg/l in September. The AWQS for PCE is 5.0 µg/l. The RI report was finalized in October.

2008: The PRAP was finalized by ADEQ after going out for public comment, and a public meeting was held in July. The final ROD was presented during the CAB’s last meeting in November. PCE concentrations in wells ranged from 2.1 µg/l to non-detect (<0.50 µg/l). All wells in the site were below the AWQS for PCE.

2010: ADEQ collected groundwater samples from five Tonto & Cherry wells in April. PCE, TCE, c-1,2-DCE and VC concentrations in wells TC-1, TC-2 and TC-3 were all non-detect. In monitor well TC-4, concentrations of PCE, TCE and VC were also non-detect. However, c-1,2-DCE was detected at a concentration of 42 µg/L, well below the AWQS of 70 µg/L.

2011: Groundwater sampling in September indicated PCE was not detected above the laboratory reporting limit of 0.5 µg/l in any of the five wells sampled at the site.

TCE was non-detected above the AQWS of 0.5 µg/l in any of the five wells sampled at the site. VC was detected at a concentration of 1.71 µg/l in monitor well TC-4. The AWQS for VC is 2.0 µg/l C-1,2-DCE was present at a concentration of 20.3 µg/l in monitor well TC-4

2012: Annual groundwater sampling was conducted in September.

2013: Annual groundwater sampling was conducted in Feb.. Detected concentrations of PCE, TCE, VC and c-1,2-DCE have been below their respective AWQSs since the June 2006. Historical groundwater monitoring data suggests that MNA achieved cleanup of the site to concentrations below AWQSs.
ADEQ has reviewed the remedy and determined that site completion criteria has been met and that cleanup levels have been achieved. On December 27, 2013, ADEQ issued a closeout ROD demonstrating that the site completion criteria used to evaluate the selected remedial action for VOC contaminated groundwater at the site has been achieved. The decision in the closeout ROD is based upon site previous activities and investigations conducted and performed for this site.

Contaminants:

The current contaminants of concern in groundwater include tetrachloroethene (PCE) and trichloroethene (TCE). Contaminants of concern at the site may change as new data becomes available. No drinking water wells are threatened by this contamination plume.

Public Health Impact:

The AWQS for PCE is 5.0 µg/l. As of the March 2008 groundwater sampling, all domestic wells in the site are currently below the AWQS. The Arizona Department of Health Services stated in their health consultation that “…use of the water for domestic purposes other than drinking was not likely to cause any adverse health effects.”

Site Hydrogeology:

The aquifer beneath the site is in the Payson Granite. The hydrogeology of the Payson area has been defined in the site Hydrogeologic Conceptual Model (HCM) based on drilling and testing activities.

Interested parties can review site information here on this page and at the ADEQ Record Center located at 1110 W. Washington Street, Phoenix, Arizona. Please contact (602) 771-4380 or (800) 234-5677 ext. 6027714380 for hours of operation and to schedule an appointment.
To review site information at a location near you, please contact the designated Community Involvement Coordinator.